The present invention relates to an ink jet recording method and apparatus and a recording head therefor in which liquid droplets are ejected using thermal energy onto a sheet of paper, resin sheet or cloth or another recording material.
In an ink jet recording method, the recording medium (ink), which is in the form of a liquid material or a heat-soluble solid material is deposited on the recording material, using thermal energy. The recording method has the advantages of high speed recording (relatively high recording quality and low noise). In addition, the method is relatively easily applicable to color image recording on a plain sheet of paper or cloth or the like. A further advantage is that the size of the apparatus is small.
The ink jet recording apparatus using this method comprises a recording head which has ejection outlets for ejecting the ink in the form of droplets, ink passages communicating with the ejection outlets and energy generating means for applying ejection energy to the ink in the liquid passages. U.S. Pat. No. 4,723,129 discloses a method in which the energy generating means is in the form of an electrothermal transducer, and the thermal energy produced by the application of an electric pulse is applied to the ink so as to eject the ink.
In the recording method disclosed in the above U.S. Patent, the ink, having received the thermal energy, is subjected to a state change, which causes a quick volume change, by film boiling of the liquid. By the development and contraction of a bubble, the ink is ejected through the ejection outlet at one end of the recording head. The ejected droplets of the ink are deposited onto the recording medium to form an image. According to this recording method, ejection outlets may be a arranged at high density in a recording head, and therefore, high speed, high resolution and high quality images can be recorded. A recording apparatus using this method can be used as a copy machine, printer, facsimile machine or other information outputting means.
Japanese Laid-Open Patent Application No. 161935/1979 discloses that ink in an ink chamber is gasified by a cylindrical heat generating element, and the gas is ejected through an ink ejection outlet together with ink droplets. According to this method, the gas and fine droplets or splashed, resulting in a low quality image. In addition, the ink is further gasified by the splash, resulting in the production of ink mist, which further contaminates the background of the recorded image or the inside of the recording apparatus.
Japanese Laid-Open Patent Application No. 197246/1986 discloses a modified ink jet recording method or thermal transfer recording method, in which single ink ejection is effected. In this method it is difficult to have the heat generating element come into complete contact with the recording material, and therefore, the thermal efficiency tends to decrease as compared with an ink jet recording method using a recording head having the conventional ejection outlets. Therefore, this method is not suitable for high speed recording.
On the other hand, U.S. Pat. No. 4,638,337 discloses, as prior art, a recording method in which a bubbles communicates with the ambient air. However, the communication between the bubble and the ambience occurs adjacent the heat generating element, not adjacent the ejection outlet. For this reason, this method easily introduces air into the neighborhood of the heat generating element, resulting in unstable ink ejection, as described in the patent. Japanese Laid-Open Patent Application No. 185455/1986 discloses that liquid ink contained in a small clearance area formed between a plate having a small opening and a heat generating member head is heated by the heat generating member, so that the ink is ejected in the form of a droplet through the small opening by a bubble produced by film boiling, and the gas constituting the bubble is also ejected through the small opening, to effect the recording of an image on a recording sheet.
Japanese Laid-Open Patent Application No. 249768/1986 discloses an ink jet recording apparatus in which thermal energy is applied to liquid ink to produce a fairly large bubble to eject a small droplet of ink by the expansion force of the bubble, wherein the gas constituting the bubble is also ejected into the ambience.
However, the above-discussed Japanese Laid-Open Patent Applications Nos.xe2x80x94161935/1979, 185455/1986 and 249768/1986 have in common the characteristic that the gas constituting the bubble is ejected into the ambience in the form of a fine ink mist together with the main ink droplet. As a result, the gasified ink produced by the gas ejection splashes to produce an ink mist, resulting in background contamination of the recording sheet or contamination inside the apparatus.
In order to solve the above problems of the ink jet recording system, U.S. Ser. No. 692,935 has proposed that the bubble produced by the film boiling is caused to communicate with the ambience adjacent to the ejection outlet (a communication ejection system).
With this communication ejection system, the gas constituting the bubble is not ejected with the ink droplet, so that the production of the splash or mist is reduced, and therefore, the contamination of the recording material and the inside of the apparatus can be prevented.
A fundamental characteristic of the communication ejection system is that the ink downstream of the bubble formation position is, in principle, all ejected out. Therefore, the amount of ejected ink can be determined on the basis of characteristics of the structure of the recording head, such as the distance from the ejection outlet to the bubble formation position. As a result, in the communication ejection system, the ejection amount can be stabilized without employing or being affected by the influence of the ink temperature or the like.
However, in the case in which the heat generating portion and the ejection outlet portion are positioned opposed to one another, the formed bubble is sometimes not stably communicated with the ambience, with the result that ejection performance changes.
On the other hand, a liquid jet recording method using thermal energy has various advantages, and the various types of image processing are effected in a manner similar to other types of dot matrix printers. In such processing, a gray scale is provided depending on the number of dots, or a great number of dots are concentrated on a predetermined area to control the tone level. If this method is used, another problem arises.
When recording is performed with a plurality of liquid droplets and when 4 level recording is effected for 4 kHz bi-level recording, 4xc3x973=12 kHz is required. If the recording head is operated at such a high frequency, the temperature of the recording head increases significantly. In addition, a large temperature difference is produced depending on the frequency used, resulting in a very large variation in the droplet size.
In liquid jet ejection using thermal energy, the volume of the droplet and the ejection speed thereof easily change depending on changes in the properties of the liquid due to thermal energy, and this tendency is mots marked if a larger number of liquid droplets are concentrated in a small area.
At present, these problems have been avoided by decreasing the recording speed, because otherwise the image processing and the performance of the recording head are not adequate. Or, alternatively, the recording operation is interrupted for the purpose of promoting the fixing of the liquid on the recording material. Therefore, the above problems have not appeared as significant problems. However, if higher image quality is required, such that the number of droplets concentrated on the same area must be increased, and the volume of a single droplet made smaller and more stabilized, then these problems will reappear. The variations in the liquid droplets in the present recording head occur not only in the long term but also within a single line of printing. Before high image quality can be achieved, these problems have to be solved.
Accordingly, it is a principal object of the present invention to provide an ink jet recording method and apparatus, and a recording head using the same, of a communication ejection type, in which the ink droplet formation is further stabilized to improve the image quality.
It is another object of the present invention to provide an ink jet recording method and apparatus and a recording head using the same in which the ink meniscus, which is retracted far behind the ejection, outlet by the communication ejection is quickly returned to the original position.
It is a further object of the present invention to provide an ink jet recording method and apparatus, and a recording head using the method, in which the ejection performance is improved to enable higher frequency ink elections, in which the liquid droplet is ejected at high speed, with stability and substantially without volume change of the liquid droplet even when the recording system is such that a large number of droplets are ejected during a short period of time, as in the case where a large number of droplets are concentrated on a small area or when high speed printing is carried out by multi-nozzles.
According to an aspect of the present invention, there is provided a liquid jet recording method using thermal energy to eject liquid from a liquid passage through an ejection outlet, the liquid passage being provided with a heat generating resistor, wherein at least one of the following conditions is satisfied:
0.1xe2x89xa6H/Lxe2x89xa60.9
R/Lxe2x89xa70.5
xc3x8/Wnxe2x89xa61.0
S/Shxe2x89xa63.0
where L is a distance between the heat generating resistor and the ejection outlet, H is a height of the liquid passage. R is a maximum diameter of the ejection outlet, xc3x8 is a converted diameter of the ejection outlet, Wn is a passage width of a portion where the heat generating resistor is disposed, S is an area of the ejection outlet, and Sh is an area of the heat generating resistor; wherein a bubble created by the heat generating resistor communicates with the ambience.
According to another aspect of the present invention, there is provided a recording head comprising: a liquid ejection outlet, a liquid passage in communication with the ejection outlet, and an electrothermal transducer having a heat generating resistor for supplying thermal energy to the liquid in the passage to eject the ink through the ejection outlet by creation of a bubble in the liquid in the liquid passage, wherein at least one of the following conditions is satisfied:
0.1xe2x89xa6H/Lxe2x89xa60.9
R/Lxe2x89xa70.5
xc3x8/Wnxe2x89xa61.0
S/Shxe2x89xa63.0
where L is a distance between the heat generating resistor and the ejection outlet, H is a height of the liquid passage, R is a maximum diameter of the ejection outlet, xc3x8 is a converted diameter of the ejection outlet, Wn is a passage width of a portion where the heat generating resistor is disposed, S is an area of the ejection outlet, and Sh is an area of said heat generating resistor; wherein a bubble created by the heat generating resistor communicates with the ambience.
According to a further aspect of the present invention, there is provided a liquid jet recording method in which liquid is ejected through an ejection outlet from a liquid passage by thermal energy from a heat generating resistor, wherein a flow resistance element is provided upstream of the heat generating resistor in the liquid passage, and a bubble created by the heat generating resistor communicates with the ambience adjacent the ejection outlet, when the liquid is ejected through the ejection outlet.
According to a further aspect of the present invention, there is provided a liquid jet recording method in which liquid is ejected through as ejection outlet by thermal energy provided by a heat generating resistor by creating a bubble in the liquid in the liquid passage, wherein the bubble communicates with the ambience adjacent the ejection outlet, and one pixel is recorded by plural droplets of the liquid ejected through the ejection outlet.
The present invention is suitably usable under one or more of the following conditions:
(1) When the ink is ejected, the ink is not disconnected into two portions by the bubble.
(2) When the bubble is brought into communication with the ambience, the internal pressure of the bubble is not higher than the ambient pressure.
(3) When the bubble is brought into communication with the ambience, the acceleration of the front end of the bubble toward the ejection outlet is not positive.
(4) When the bubble is brought into communication with the ambience, 1a/1b greater than 1 is satisfied, where 1a is distance between an ejection outlet side edge of the flat heater and a front end of the bubble, and 1b is a distance between such an edge of the heater as is opposite the outlet side edge and the rear end of the bubble.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.